Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: DEVICE FOR DETECTING ELECTRICAL POTENTIALS USING
FRONTAL ELECTRODES
TECHNICAL FIELD
[0001] Embodiments relate to a device for detecting electrical potentials
using frontal electrodes. In particular, embodiments involve positioning of at
least three electrodes on human forehead positions.
BACKGROUND
[0002] For medical diagnostic purposes, it can be useful to determine
the sleep stages experienced by a person during sleep. Such sleep stage
determination has traditionally been performed in a laboratory setting, in
which the patient is asked to sleep while undergoing the testing. Under such
conditions, the patient is likely to experience abnormal sleep patterns.
[0003] The sleep stage determination is performed by affixing a
plurality of electrodes on the patient's scalp at various standard positions
according to the 10 - 20 system of electrode placement. Some electrodes
are positioned to sense electroencephalographic (EEG) signals, while other
electrodes may be positioned to detect electromyographic (EMG) signals or
electrooculographic (EOG) signals. The EEG, EMG and EOG signals may
be provided to a processing system, including, for example, a neural network
for use in determining the stage of sleep experienced by the person
according to the detected signals.
[0004] Embodiments attempt to address or ameliorate one or more of
the disadvantages or shortcomings associated with existing devices for use
in sleep stage determination, or to at least provide a useful alternative
thereto.
SUMMARY
[0005] Embodiments relate to devices for detecting electrical potentials
corresponding to biological signals. The device comprises a flexible member
for positioning over a forehead area of a human head and first, second and
third electrodes located on the flexible member. The first electrode is
located
in a projecting portion of the flexible member to be positioned adjacent a
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nasion area of the head. The second electrode is to be positioned over a
first lateral forehead area. The third electrode is to be positioned over a
second lateral forehead area opposite the first lateral forehead area. The
second and third electrodes have a separation of between 35 mm and 200
mm.
[0006] Conductors may be formed on the flexible member for
electrically coupling the first, second and third electrodes to an output
connector. The second and third electrodes may be located on opposite
lateral wings of the flexible member and the output connector may be
coupled to one of the lateral wings. The first electrode may be positioned
immediately above the nasion, between the eyebrows.
[0007] The device may further comprise a fourth electrode located on
the flexible member intermediate the second and third electrodes for
positioning over a central forehead area. The fourth electrode may be
positioned above the first electrode and both the first and fourth electrodes
may be aligned with or positioned along a vertical centerline of the head.
The fourth electrode may be positioned lower on the forehead than an Fz
electrode position. The fourth electrode may act as a reference or ground
electrode. If the fourth electrode acts as a ground electrode, the first
electrode may act as a reference electrode.
[0008] The second and third electrodes may be positioned on the
forehead higher than and laterally beyond Fpl and Fp2 positions. The
second, third and fourth electrodes may be positioned along a line extending
laterally across the forehead. The first, second and third electrodes may be
positioned in a triangular configuration, such as an isosceles triangular
configuration. The first, second, third and fourth electrodes may be
positioned in a T-shaped configuration.
[0009] The conductors may comprise a printed flexible material. The
conductors may comprise silver and/or silver chloride, for example. The
conductors may be formed on a substrate of the flexible member. The
conductors and substrate may be covered by an insulation material in areas
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where the electrodes are not formed on the flexible member. The insulation
material may have a double-sided adhesive foam layer thereon for adhering
the device to the forehead and fixing the electrodes in position against the
forehead.
[0010] Each electrode may have a layer of conductive gel disposed
thereon for facilitating conduction of electrical signals or potentials on or
below the skin to the respective electrode. The device may have a protective
layer on an underside thereof for protecting the conductor gel and adhesive
foam prior to application of the device to the forehead. The protective layer
is readily removable from the device.
[0011] The second and third electrodes may have a lateral separation
of about 70 to 110 mm. The separation may be 80 to 100 mm. The
separation may be about 90 mm.
[0012] The first and fourth electrodes may have a separation of about
35 to 55 mm. The separation may be about 40 to 50 mm. The separation
may be about 44 mm.
[0013] The second and third electrode may have a portion of adhesive
material disposed around the respective electrode for affixing the respective
electrode to the skin of the forehead.
[0014] The biological signals may be generated during a sleep study.
The device may be used to determine a sleep stage of a wearer of the
device. The device may be used to determine an ischemia of a wearer of the
device. The device may be used to determine a level of consciousness of a
wearer of the device.
[0015] A method of detecting electrical potentials corresponding to
biological signals may be comprised of positioning the device over the
forehead area so that the first electrode is positioned adjacent the nasion
area, the second electrode is positioned over the first lateral forehead area
and the third electrode is positioned over the second lateral forehead area;
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and detecting the electrical potentials using the first, second and third
electrodes.
[0016] Another particular embodiment relates to a sensing device for
use in sleep stage determination using frontal electrodes. The device
comprises: a flexible member for positioning over a forehead area of a
human head, the flexible member having opposed lateral wings and a
projecting portion; a plurality of electrodes located on the flexible member
for
positioning laterally across the forehead; and an electrode located on the
projecting portion for positioning adjacent a nasion area.
[0017] Yet another particular embodiment relates to a sensing device
for use in sleep stage determination using frontal electrodes. The device
comprises: a flexible member for positioning over at least part of the
forehead of a human head, the flexible member being approximately T-
shaped; and a plurality of electrodes located on the flexible member for
positioning over areas on or adjacent the forehead, at least one electrode
being located on the flexible member at a bottom of the T-shape for
positioning adjacent a nasion area when the device is positioned on the head
in an upright position.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Embodiments are described in further detail below by way of
example only, with reference to the accompanying drawings, in which:
[0019] Figure 1 is a front view of a sensing unit shown located on a
human forehead, according to some embodiments;
[0020] Figure 2 is an illustrative side cross-section of the sensing unit of
Figure 1, taken along the line A-A;
[0021] Figure 3A is a representative side view of a human head,
showing standard electrode positions and electrode positions according to
some embodiments;
[0022] Figure 3B is a representative plan view of a human head
corresponding to Figure 3A;
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[0023] Figure 4 is a schematic representation of the relative positions of
electrodes on the sensing unit; and
[0024] Figure 5 is an illustrative partial side cross-section of the sensing
unit according to further embodiments.
DETAILED DESCRIPTION
[0025] Referring now to Figures 1 to 5, embodiments of a device for
use in measuring biological signals are shown and described. In the
drawings and description, like reference numerals are used to indicate like
features, functions and/or elements as between the drawings.
[0026] In this description, reference to terms implying a directional
orientation, such as lateral, vertical, below, above or downward, are intended
to be viewed as if the embodiments are positioned on a forehead of a human
head, while that head is upright. Accordingly, "vertical" is intended to
denote
directions from the top of the skull toward the neck, while "lateral" is
intended
to denote positions or directions to one side of a midline of the head
extending along the frontal line of symmetry of the face (i.e. perpendicular
to
vertical). Thus, "lateral" as applied to the forehead means extending across
the forehead between the eyebrows and the hairline and, depending on the
shape of the particular forehead, extending around toward the upper temple
area.
[0027] It should be understood that terms used herein that imply
direction or orientation, such as those mentioned above, are used for ease of
description only and are not intended to be a limitation on the described
embodiments when they are not in use on the forehead.
[0028] Referring in particular to Figure 1, there is shown a sensing unit
110 positioned on the forehead of a human head 10. Sensing unit 110 has
an electrode array including four electrodes El, E2, E3 and E4 formed
thereon for overlying exposed skin surfaces of the forehead and nasion
areas. Electrodes El, E2, E3 and E4 are used to detect EEG, EMG and
EOG signals, for example during a sleep study or for determining the
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occurrence of our ischemia or determining the level of consciousness of the
wearer.
[0029] Sensing unit 110 comprises a flexible plate-like member 120
formed roughly in a squat T-shape when viewed from the front while worn on
the head 10. A lower portion 125 of flexible member 120 projects
downwardly from the substantially laterally extending body of flexible
member 120. Lower portion 125 houses electrode E3 so as to be positioned
to at least partly overlie the nasion area or an area adjacent thereto.
Depending on the forehead structure of the head 10, electrode E3 may be
positioned slightly above the nasion area, but generally on a centre line
extending vertically through the forehead intermediate the eyes and
eyebrows.
[0030] Electrodes El, E4 and E2 are spaced laterally across sensing
unit 110. Electrode E4 acts as a ground electrode relative to the measured
signals from electrodes El, E2 and E3. Electrodes El and E2 are positioned
in laterally extending wings 127 and 128 located on respective right and left
sides of the head 10 (as seen from the patient's perspective). Electrodes El
and E2 and wings 128 and 127 are positioned widely (laterally) so that, for
most forehead sizes and structures, the electrodes El, E2 are positioned on
the forehead above and laterally beyond a vertical centerline through the
eyes. The greater lateral spacing of electrode El and E2 allows the sensing
of a greater amount of relevant EEG data.
[0031] Ground electrode E4 is positioned generally centrally on sensing
unit 110 within a central area 126 of flexible member 120 that connects to the
internally extending wings 127 and 128 and lower portion 125.
[0032] As shown in Figure 1, flexible member 120 has a connector limb
132 extending from a left side (seen from the patient's perspective) thereof
and a connector 130 at an end of connector limb 132. Connector 130 is
arranged to electrically couple conductors 122 extending through sensing
unit 110 to a processing unit (not shown), thereby forming an electrical
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connection between the processing unit and the electrodes El, E2, E3 and
E4 to which conductors 122 are electrically coupled.
[0033] According to one embodiment, sensing unit 110 is formed
mostly of flexible materials for placement on a forehead structure and for
generally conforming to the shape of the forehead structure. Certain parts of
sensing unit 110 (for example, those around the electrodes) have an
adhesive substance, such as a foam adhesive layer, on an underside
thereof, for affixing the sensing unit 110 to the forehead prior to conducting
the sleep study. Flexible circuitry, in the form of conductors 122 extends
through sensing unit 130 between the electrodes El to E4 and connector
130. Thus, sensing unit 110 can be used with forehead structures of varying
shapes and sizes due to its flexibility and ability to conform and adhere to
such varying forehead structures, as required.
[0034] Sensing unit 110 is shown in Figure 2 in partial cross-section,
taken along line A-A of Figure 1. Flexible member 120 employs a substrate
210 of a flexible material such as a medical grade polyester film (or other
material having similar properties).
[0035] Flexible member 120 has a substrate 210, which forms the top
(or upper or outer) layer facing away from the forehead. Substrate 210 has
sufficient rigidity to form the base for flexible circuitry to be printed
thereon
and enable subsequent conductive and insulative layers to be formed
thereon, while having sufficient flexibility to enable the entire flexible
member
120 to bend to generally conform to the shape of the forehead to which it is
to be affixed.
[0036] The substrate 210 may be about 3 to 8 thousandths of an inch
thick, for example. Adhesive 270 is used to affix at least a part of the
flexible
member 120 to the forehead structure. This adhesive 270 is provided on a
layer of medical grade adhesive foam 260 of about 1/32 of an inch thickness.
The foam 260 is adhered to an insulation layer 220 on the substrate 210 on
one side with a relatively strong adhesive 240 and has adhesive 270, which
is of relatively less strength, on the opposite side for removable attachment
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to the test subject. The electrodes El to E4 may comprise a silver or silver
chloride layer formed on the substrate. The substrate 210 has flexible circuit
tracings formed thereon for constituting the conductors 122 between
electrodes El to E4 and output connector 130. Such circuit tracings may
comprise silver and preferably have a dielectric layer (such as insulation
layer 220) formed thereover.
[0037] Prior to affixation to the forehead, sensing unit 110 may have
backing sheets on those parts of sensing unit 110 that have an adhesive
substance on their undersides for adhesion to the skin. Each such backing
sheet is removed immediately prior to adhesion of the relevant part of
sensing unit 110 to the corresponding forehead areas. For electrodes El to
E4, an area of conductive gel, such as hydrogel, is interposed between the
respective electrode and the skin surface (instead of the adhesive foam), for
facilitating conductivity of electrical signals between the electrodes El to
E4
and the skin.
[0038] Sensing unit 110 is a generally flat device, as viewed from the
user's perspective, prior to affixation to the test subject. However, sensing
unit 110 does have several layers, as described above. In use of sensing
unit 110, and with the backing sheets removed, the adhesive foam parts and
electrodes El to E4 are positioned to lie against the skin. These skin contact
surfaces may be conveniently referred to as being formed on the underside
of the sensing unit 110. Printed labeling, including affixation instructions,
may be provided on the side of sensing unit 110 that does not contact the
skin.
[0039] Electrodes El to E4 are formed on substrate 210, either directly
or on a thin priming or separation layer (not shown) coating the underside of
substrate 210. Electrodes El to E4 are electrically coupled to output
connector 130 via conductors 122 in the form of flexible circuit tracings
formed on substrate 210. As with electrodes El to E4, conductors 122 may
be directly formed on substrate 210 or may be separated therefrom by a
priming or separation layer. Portions of flexible member 120 that are not to
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be exposed to the forehead (such as conductors 122) are covered by
insulation layer 220.
[0040] In the embodiment shown in Figure 2, electrode E4 comprises a
silver chloride layer 230 on its outer face for facilitating conductivity with
the
skin via a conductive gel in contact with electrode E4. The conductive gel is
provided as a liquid hydrogel and is impregnated into a porous foam sponge
250 that contacts the skin when the sensing unit 110 is positioned on the
patient's forehead. Sponge 250 is adhered to substrate 210 by an adhesive
layer 225 disposed around the electrodes. In order to allow for compression
of the sponge during skin contact, a gap is formed on either side of the
sponge 250 between the sponge 250 and the foam layer 260.
[0041] In an alternative embodiment, a substantially more viscous
conductive gel can be used instead of the sponge 250 and liquid hydrogel, in
which case the adhesive layer 225 and the compression gap are not
required. The above impregnated sponge arrangement and the viscous
hydrogel arrangement are both commercially available from Vermed, Inc. of
Bellows Falls, Vermont, USA.
[0042] Adhesive layer 270 and conductive sponge 250 are covered by
a protective backing sheet or layer (not shown) so that the adhesive and
conductive qualities of the adhesive layer 270 and conductive sponge 250
are preserved until application of flexible member 120 to the forehead. The
total thickness of substrate 120 may be in the range of 0.7 to 1.5
millimeters,
approximately.
[0043] The embodiments shown in Figures 2 and 5 are not to scale, is
for purposes of illustration only and some variations or modifications may be
made, depending on the specific requirements of the sensing unit
embodiment and methods of forming it.
[0044] While the sensing unit embodiments shown and described
herein generally show a unitary flexible member including two wings and
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projecting portion, each of the areas or portions of the sensing unit having
electrodes may be formed on a separate, but connected, substrate.
[0045] In an alternative embodiment of sensing unit 110, metallic disk
electrodes may be used with a flexible member formed of molded plastic,
such as a polyvinylchloride (PVC) plastic. In such an embodiment, the
plastic is preferably relatively thin and flexible to accommodate the contours
of the wearer's forehead, while having sufficient structural integrity and
rigidity to maintain the electrodes in their respective positions. Such a
molded plastic flexible member may employ a suitable adhesive to secure it
in place on the forehead. Alternatively, or in addition, a strap or other
mechanical means may be used to secure the sensing unit 110 in place on
the wearer's forehead.
[0046] Referring in particular to Figures 3A, 3B and 4, the positioning of
electrodes El, E2, E3 and E4 is described in further detail. Figures 3A and
3B indicate the likely positions of electrodes El to E4 on a human head,
relative to the standard 10 - 20 electrode positions. As can be seen from
Figures 3A and 3B, reference electrode E3 is positioned adjacent the nasion
area. Electrode E3 is located on flexible member 120 so that, for most
forehead structures, it will be positioned immediately above the nasion and in
between the eyebrows. Electrode E3 is thus positioned on the vertical
centerline of the head in a position lower than the line extending through
frontal positions Fpl and Fp2.
[0047] Electrode E4 is positioned on the midline (vertical centerline)
below frontal position Fz but above the frontal line extending through frontal
positions Fpl and Fp2. Electrodes E3 and E4 are separated by a distance
X, as shown in Figure 4, where X may be about 35 to 70 mm. In some
embodiments X may be between about 35 mm and 55 mm. In some
embodiments, X may be about 40 to 50 mm. In further embodiments, X may
be about 44 mm. The distance X can be measured as the separation of
electrodes E3 and E4 or it can be measured as the vertical separation of
electrode E3 from the lateral line extending between electrodes El and E2.
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This latter configuration may be applicable where electrode E4 is not used or
is not positioned along the lateral line between electrodes El and E2.
[0048] As shown in Figure 4, electrodes El to E4 are arranged in a T-
shaped configuration, with reference electrode E3 at a bottom of the T and
electrodes El, E2 and E4 forming the top line of the T. In alternative
embodiments, the electrode configuration need not be strictly T-shaped. For
example, ground electrode E4 may be shifted up or down so that it is not
strictly in line with electrodes El and E2.
[0049] Further, electrodes El, E2 and E3 are arranged in a triangular
configuration, where the distance between electrodes El and E3 is the same
as the distance between electrodes E2 and E3, but may or may not be the
same as the distance between electrodes El and E2. Thus, electrodes El,
E2 and E3 are arranged in an isosceles triangular configuration. This
configuration allows the electrodes to be arranged in sensing pairs El - E3
and E2 - E3 to sense EEG, EOG and EMG potentials, while sensing
electrode pair El - E2 is also arranged to sense EEG, and EOG potentials.
The El - E3 and E2 - E3 electrode pair orientations may be configured to be
substantially orthogonal to each other.
[0050] Electrodes El and E2 are each laterally separated from
electrode E4 by a distance Y that may be the same as distance X or may be
different therefrom. The total distance (2Y) between electrodes El and E2
is, according to some embodiments between about 35 and 200 mm. In other
embodiments, the separation of electrodes El and E2 is between about 50
and 150 mm. In further embodiments, the separation is between about 70
and 110 mm. In other embodiments, the separation of electrodes El and E2
is about 80 to 100 mm. In further embodiments, the separation is about 90
mm.
[0051] In determining possible configurations and separations of
electrodes El, E2, E3 and E4, there is a lower bound of about 35 mm
separation between any two electrodes. This lower bound is determined
experimentally as the minimum separation needed to produce two distinct
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signals. It is also constrained physically by the dimensions of the electrodes
and the need to keep them sufficiently electrically separated to avoid
creation
of a salt bridge through the skin.
[0052] An upper bound of about 200 mm for the lateral spacing of
electrodes El and E2 is also applicable and takes into account the
desirability of avoiding the hairline and of avoiding electrode placement on
the side of the skull. It is generally desirable to place an electrode in such
a
way that it does not make contact with a pillow when the wearer is sleeping
on his or her side. Otherwise, contact of the electrode with the pillow will
introduce artifacts in the sensed electrical potentials at the electrode when
the patient moves (known as a motion artifact) and may result in an
uncomfortable pressure point for the wearer.
[0053] An upper bound on the vertical separation of the third and fourth
electrodes may be about 70 millimeters, which is on average the maximum
distance between the nasion and the hairline at the lateral centre of the
forehead.
[0054] Between the upper and lower bounds of the separations of the
electrodes are preferred dimensions for distance Y and distance X as
described above, although some variation of these distances can be used
while remaining within the upper and lower bounds described above. Such
preferred distances may be, for example, about 90 millimeters for the
separation between electrodes El and E2, which equates to 2Y. This
spacing provides sufficient spacing of electrodes El and E2 so that, on
average, those electrodes are positioned laterally beyond the vertical centre
lines of the eyes and the fpl, fp2 positions, while not extending so far as to
cause electrodes El and E2 to be placed on the sides of the head 10. For a
lateral separation of about 90 millimeters between electrodes El and E2, a
vertical separation of about 44 or 45 millimeters between E3 and the lateral
line extending between electrodes El and E2 may be used, regardless of
whether reference electrode E4 is employed. Such a vertical separation of
electrode E3 from electrodes El and E2 allows electrodes El, E2 and E3 to
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be configured roughly as an isosceles right angled triangle, where the line
between electrodes El and E3 is roughly perpendicular to the line between
electrode E2 and E3. Such a configuration is not essential, however, and
variations of the triangular configuration of electrodes El, E2 and E3 may be
employed to similar effect.
[0055] Electrodes El and E2 are located on flexible member 120 so as
to be positioned on the forehead at forehead locations above and laterally
beyond standard frontal positions Fpl and Fp2, respectively. This wider
spacing of electrodes El and E2 across the frontal area allows for a greater
range and quality of EEG signal activity to be detected than if the standard
Fpl and Fp2 positions were used. This greater range compensates for the
lack of the commonly used reference electrode positioned at Al or A2 behind
the ear.
[0056] The specific configuration of electrodes El, E2 and E3 allows for
simultaneous sensing of EEG, EOG and EMG signals using a single
electrode assembly on a flexible member that is easily applied by a patient to
his or her own forehead prior to self-initiation of the sleep study. Thus,
sensing device 110 is easily applied in a home setting without the need for
the patient to be studied in an artificial environment and without the need
for
a medical technician to affix the electrodes to the patient's head 10.
[0057] In alternative embodiments of sensing unit 110, one or more of
electrodes El to E4 may comprise a needle electrode specifically configured
for EMG signal detection. Alternatively, or in addition, one or more of
electrodes El to E4 may have a wireless transmitter associated therewith
(instead of a conductor 122) for transmitting wireless signals to a nearby
receiver, such as is described in co-pending, co-owned United States Patent
Application Serial No. 11/130,221, entitled "Wireless Physiological Monitoring
System", filed May 17, 2005, the entire contents of which is hereby
incorporated by reference.
[0058] Although not shown in Figure 1, some embodiments of sensing
unit 110 may have a strap attachable to each lateral wing 127, 128 for
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securing sensing unit 110 to head 10. Such a strap may be in addition or
alternative to adhesive 270 for securing sensing unit 110 in place. In place
of
a strap, other means for securing the sensing unit to the head 10 may be
employed.
[0059] In further embodiments, as depicted in Figure 5, electrodes El
to E4 are removably attachable to flexible member 120. In these
embodiments, electrodes El to E4 are formed as disk-shaped electrodes
that have male snap connector parts 504 on a back surface thereof for
engaging a corresponding female snap connector part 502 positioned on
flexible member 120. In these embodiments, conductors 122 are electrically
coupled (for example by a silver chloride layer 230) to the female snap
connector parts 502, which form a mechanical and electrical connection with
the electrodes via the male snap connector parts 504 on each electrode.
[0060] In these embodiments, the underside of flexible member 120
may or may not employ an adhesive to affix the flexible member 120 to the
forehead. If no adhesive is used, a strap or band can be used to secure the
flexible member 120 in the appropriate location. In order to affix the
electrodes El to E4 to the appropriate locations on the forehead and nasion
areas, each electrode is provided with an annular portion of adhesive foam or
other substance around the outside of the conductive contact surface
(conductive gel 250) of the electrode. Alternatively, the conductive gel on
the
contact surface of the electrodes may have sufficient adhesive properties to
obviate the use of adhesive foam portions around the electrodes. Examples
of commercially available "snap connector" electrodes that can be used with
these electrodes include those sold by Vermed under their Versa-TrodeTM
product line.
[0061] The removably attachable electrode embodiments allow the
flexible member 120 to be reusable while the electrodes can be disposed of
after each use. In these embodiments, the flexible member 120 may be
comprised of a material having greater flexibility and/or deformation
properties than the polyester film or PVC described above. A suitable
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material may comprise a cloth or other woven material. Alternatively, the
flexible member 120 may be comprised of a relatively more rigid material,
such as PVC, although this rigidity is not strictly required if each electrode
is
held in place on the skin by the portion of adhesive material 270 surrounding
it.
[0062] Figure 5 illustrates embodiments of sensing unit 110 that employ
"snap on" electrodes for electrodes El, E2, E3 and optionally E4. Each such
snap on electrode comprises the male connector part 504 connected to a
substrate 510 that has adhesive layer 270 on its outward skin facing surface.
The male connector part 504 may have a silver chloride layer 230 deposited
on its outward (skin facing) side, over which is positioned a conductive gel
or
foam layer 250. Thus, the male connector part 504, silver chloride layer 230
and female connector part 502 effectively form the electrode, with the male
connector part 504 being carried on substrate 510 for removable connection
to sensing unit 110 via female connector part 502.
[0063] Further, according to some embodiments, in order for sensing
unit 110 to accommodate foreheads of different sizes, substrate 210 may
have a group of closely spaced or adjacent female connector parts 502 (in
electrical connection with a single conductor 122), one of which will receive
the male connector part 504 of the electrode when the sensing unit 110 is in
use.
[0064] Although Figure 5 depicts one form of snap-fitting connection, it
should be understood that other forms of electro-mechanical connection may
be employed to provide removable connection of the electrode to the sensing
unit 110.
[0065] While the configuration of the electrode array of sensing unit 110
is arranged in a T-shaped configuration, alternative configurations, for
example where the central ground electrode E4 is positioned higher or lower,
may be employed. However, electrode configurations that necessitate
placement of one of the electrodes over a hair-covered part of the scalp are
less desirable than those that allow placement of the electrodes over hairless
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areas of the scalp. Thus, shapes analogous to a T-shape, such as a cross-
shape, Y-shape or other shapes having laterally extending wings and a
downwardly projecting portion, may be employed to a similar effect to the
embodiments using a T-shaped electrode configuration and a flexible
member. In one embodiment, the lateral wings of the flexible member 120
may extend further laterally and droop down to cover the temple areas on
either side of the head. This allows additional electrodes to be placed over
the temple areas for increased EEG sensing capability.
[0066] While sensing unit 110 is described as being applicable for use
in sleep stage determination, it should be understood that it can also be used
in connection with other apparatus or software to record other results of
diagnostic significance. One example of such other apparatus is a mask for
providing continuous positive airway pressure (CPAP) to the patient, such as
is described in United States Patent Application Serial No. 11/131,284.
Embodiments may also be used within the context of an intensive care unit
(ICU), for example to assist in detection of a seizure, stroke, ischemia,
burst-
suppression or brain hemorrhage or for use in determining a level of
consciousness, sedation or delirium of a patient.
[0067] According to alternative embodiments, additional sensors, which
may be electrodes or other forms of sensors, may be provided for positioning
at other locations on the head. For example, an additional electrode may be
placed behind or in front of the ear or ears, for use as active or reference
electrodes. Such additional sensors may be coupled to flexible member 120
for electrical connection to the processing unit via connector 130.
Alternatively, a separate connector may be used for electrically coupling the
additional sensor or sensors to the processing unit.
[0068] While certain embodiments described herein contemplate the
use of four electrodes El to E4 located on the flexible member 120, it should
be understood that, for each of those four electrodes, more than one
electrode may be used in place of the single electrode. In still further
embodiments, the sensing unit 110 may employ more than four electrodes at
CA 02652593 2008-11-18
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various positions on the flexible member 120. In a further alternative
embodiment, the ground electrode E4 may be omitted or its position varied.
